Combine yeast and 1/2 cup warm water in small bowl.  Let rest 5 minutes.  Heat milk, butter and sugar until warm (100° to 110°F) but butter won't all melt.  Pour into large mixer bowl with yeast mixture and 2 cups flour; beat for 2 minutes.   Add eggs, buttermilk, mashed potatoes, salt, vanilla and 1 cup flour.  Beat for 2 minutes.  Gradually add flour until a soft dough forms.  Knead on a lightly floured surface until smooth and elastic (about 8 to 10 minutes).  Place in a greased bowl, turning to coat.  Cover.

Let rise in a warm, draft-free area about 1 hour, until doubled in size.  Punch dough down; divide in half.

Roll one portion of dough on a lightly floured surface to a 12 x 18-inch rectangle.  Spread with half the butter.  Combine sugars, beverage flavourings and hazelnuts; sprinkle half of the mixture over surface.  Roll up tightly lengthwise, sealing edges.  Cut into 12 slices.  Place in greased 13 x 9-inch pan.  Repeat with remaining dough.  Cover.  Let rise 30 to 45 minutes until nearly doubled.

Bake in preheated 350°F oven for 25 to 30 minutes.  Cool for 15 minutes.  Combine icing ingredients and drizzle over rolls.